In the printing field, the impact type printer has been the predominant apparatus for providing increased throughput of printed information. The impact printers have included the dot matrix type wherein individual print wires are driven from a home position to a printing position by individual and separate drivers. The impact printers also have included the full character type wherein individual type elements are caused to be driven against a ribbon and paper or like record media adjacent and in contact with a platen.
The typical and well-known arrangement in a printing operation provides for transfer of a portion of the ink from the ribbon to result in a mark or image on the paper. Another arrangement includes the use of carbonless paper wherein the impact from a print wire or a type element causes rupture of encapsulated material for marking the paper. Also known are printing inks which contain magnetic particles wherein certain of the particles are transferred to the record media for encoding characters in manner and fashion so as to be machine readable in a subsequent operation. One of the known encoding systems is MICR (Magnetic Ink Character Recognition) utilizing the manner of operation as just mentioned.
While the impact printing method has dominated the industry, one disadvantage of this type of printing is the noise level which is attained during printing operation. Many efforts have been made to reduce the high noise levels by use of sound absorbing or cushioning materials or by isolating the printing apparatus.
More recently, the advent of thermal printing which effectively and significantly reduces the noise levels has brought about the requirements for heating of extremely precise areas of the record media by use of fast response thin film resistors. The intense heating of the selective resistors causes transfer of ink from a ribbon onto the paper or like receiving substrate. Alternatively, the paper may be of the thermal type which includes materials that are responsive to the generated heat.
Further, it is seen that the use of thermal printing is adaptable for MICR encoding of documents wherein magnetic particles are caused to be transferred onto the documents for machine reading of the characters. The thermal transfer printing approach for use in MICR encoding of documents enables reliability in operation at the lower noise levels.
The use of thermal transfer printing, especially when performing a subsequent sorting operation, can result in smearing or smudging adjacent the printed symbols or digits on the receiving substrate. This smearing can make character recognition, such as OCR (Optical Character Recognition) or MICR (Magnetic Ink Character Recognition), difficult and sometimes impossible.
The present invention provides a magnetic thermal transfer medium in the preferred form of a ribbon which eliminates or substantially reduces smearing or smudging across or adjacent the printed digits or symbols during the sorting operation.
Representative documentation in the area of magnetic thermal transfer media includes U.S. Pat. No. 3,663,278, issued to J. H. Blose et al. on May 16, 1972, which discloses a thermal transfer medium having a coating composition of cellulosic polymer, thermoplastic resin, plasticizer and a sensible dye or oxide pigment material.
U.S. Pat. No. 4,022,936, issued to R. E. Miller on May 10, 1977, discloses a process for making a sensitized record sheet by providing a substrate, coating the substrate with an aqueous composition, and then drying the coating.
U.S. Pat. No. 4,463,034, issued to Y. Tokunaga et al. on July 31, 1984, discloses a process for printing a magnetic image with a heat-sensitive magnetic transfer element that includes a foundation and a layer having a ferromagnetic substance powder meltable at 50.degree.-120.degree. C.
U.S. Pat. No. 4,533,596, issued to T. P. Besselman on Aug. 6, 1985, discloses a thermal magnetic transfer ribbon that includes a substrate and a coating containing resin, oil and wax in a binder mix which is dispersed with a magnetic pigment in a solvent solution.
U.S. Pat. No. 4,581,283, issued to Y. Tokunaga et al. on Apr. 8, 1986, discloses a heat-sensitive magnetic transfer element that includes a foundation and a layer having a melting temperature of 50.degree.-120.degree. C. and comprising a ferromagnetic substance powder, a wax and a resin.
U.S. Pat. No. 4,600,628, issued to F. Ishii et al. on July 15, 1986, discloses a thermal transfer recording medium comprising a support, an interlayer containing a cross-linking agent, and a coloring agent layer containing a coloring agent and a reactive polymer.
U.S. Pat. No. 4,628,000 issued to S. G. Talvalkar et al. on Dec. 9, 1986, discloses a thermal transfer medium which includes a sucrose benzoate transfer agent and a coloring material or pigment.
U.S. Pat. No. 4,690,858, issued to H. Oka et al. on Sept. 1, 1987, discloses a thermal transfer sheet comprising a substrate and an ink layer having a sublimable dye, a binder of high molecular weight polyamide resin from dimer acid, and an organic solvent.
And, U.S. Pat. No. 4,818,591, issued to S. Kitamura on Apr. 4, 1989, discloses a thermal transfer recording medium comprising a support, a layer containing an aqueous emulsion of a heat-fusible substance, and a colorant layer comprising an aqueous emulsion of a resin and a colorant.